diff --git a/lib/cloud/cloud_session_manager.dart b/lib/cloud/cloud_session_manager.dart
new file mode 100644
index 000000000..d902630f5
--- /dev/null
+++ b/lib/cloud/cloud_session_manager.dart
@@ -0,0 +1,143 @@
+import 'dart:async';
+import 'dart:convert';
+
+import 'package:flutter_cloud_sync/flutter_cloud_sync.dart';
+
+typedef CloudServices = ({CloudProvider? provider, CloudAuthService? auth});
+typedef CloudServicesFactory = Future<CloudServices> Function(
+    CloudServiceConfig);
+
+/// Owns one active configuration's services. The factory remains uncached.
+class CloudSession {
+  CloudSession(this.config, this.services);
+
+  final CloudServiceConfig config;
+  final CloudServices services;
+  final Set<void Function()> _onClose = {};
+  Future<void>? _closing;
+  bool get isClosed => _closing != null;
+
+  /// Consumers stop scheduling work before their network resources are released.
+  void Function() onClose(void Function() callback) {
+    if (isClosed) {
+      callback();
+    } else {
+      _onClose.add(callback);
+    }
+    return () => _onClose.remove(callback);
+  }
+
+  Future<void> close() {
+    if (_closing != null) return _closing!;
+    final done = Completer<void>();
+    _closing = done.future;
+    Future<void>(() async {
+      Object? firstError;
+      StackTrace? firstStack;
+      try {
+        for (final callback in _onClose.toList()) {
+          try {
+            callback();
+          } catch (error, stack) {
+            firstError ??= error;
+            firstStack ??= stack;
+          }
+        }
+      } finally {
+        _onClose.clear();
+        await services.provider?.dispose();
+      }
+      if (firstError != null) {
+        Error.throwWithStackTrace(firstError!, firstStack!);
+      }
+    }).then(done.complete, onError: done.completeError);
+    return done.future;
+  }
+}
+
+class CloudSessionManager {
+  CloudSessionManager(
+      {CloudServicesFactory factory = createCloudServices,
+      CloudServicesFactory? temporaryFactory})
+      : _factory = factory,
+        _temporaryFactory = temporaryFactory ??
+            ((config) => createCloudServices(config, persistSession: false));
+
+  final CloudServicesFactory _factory;
+  final CloudServicesFactory _temporaryFactory;
+  CloudSession? _active;
+  Future<void> _tail = Future.value();
+  Future<CloudSession>? _pending;
+  String? _requestedKey;
+  int _generation = 0;
+  bool _disposed = false;
+
+  Future<CloudSession> activate(CloudServiceConfig config) {
+    if (_disposed) return Future.error(StateError('Session manager closed'));
+    // Includes credentials: editing credentials must replace the session too.
+    // Never log this key, since configuration can contain passwords.
+    final key = jsonEncode(config.toJson());
+    if (_requestedKey == key && _pending != null) return _pending!;
+    _requestedKey = key;
+    final generation = ++_generation;
+    final next = _tail.then((_) async {
+      _checkGeneration(generation);
+      final previous = _active;
+      _active = null;
+      await previous?.close();
+      _checkGeneration(generation);
+      final services = await _factory(config);
+      final session = CloudSession(config, services);
+      if (_disposed || generation != _generation) {
+        await session.close();
+        throw StateError('Cloud configuration changed during initialization');
+      }
+      // Backend-specific recovery belongs in session assembly, not UI providers.
+      final auth = services.auth;
+      if (auth is BeeCountCloudAuthService) {
+        auth.setRecoveryCredentials(
+          email: config.beecountCloudEmail,
+          password: config.beecountCloudPassword,
+        );
+      }
+      _active = session;
+      return session;
+    });
+    _pending = next;
+    _tail = next.then<void>((_) {}, onError: (Object error, StackTrace stack) {
+      if (generation == _generation) {
+        _requestedKey = null;
+        _pending = null;
+      }
+    });
+    return next;
+  }
+
+  void _checkGeneration(int generation) {
+    if (_disposed || generation != _generation) {
+      throw StateError('Cloud configuration changed');
+    }
+  }
+
+  /// Draft configurations never replace the active session. Always released.
+  Future<T> withTemporarySession<T>(CloudServiceConfig config,
+      Future<T> Function(CloudSession) action) async {
+    if (_disposed) throw StateError('Session manager closed');
+    final session = CloudSession(config, await _temporaryFactory(config));
+    try {
+      if (_disposed) throw StateError('Session manager closed');
+      return await action(session);
+    } finally {
+      await session.close();
+    }
+  }
+
+  Future<void> dispose() async {
+    _disposed = true;
+    ++_generation;
+    await _tail;
+    final previous = _active;
+    _active = null;
+    await previous?.close();
+  }
+}
diff --git a/lib/cloud/sync/sync_engine.dart b/lib/cloud/sync/sync_engine.dart
index f487163dd..9101495a1 100644
--- a/lib/cloud/sync/sync_engine.dart
+++ b/lib/cloud/sync/sync_engine.dart
@@ -78,6 +78,7 @@ class SyncEngine implements app.SyncService {
   /// 状态缓存
   final Map<int, app.SyncStatus> _statusCache = {};
   bool _localChanged = false;
+  bool _disposed = false;
 
   /// WebSocket 实时监听
   StreamSubscription<BeeCountCloudRealtimeEvent>? _realtimeSubscription;
@@ -361,6 +362,9 @@ class SyncEngine implements app.SyncService {
 
   /// 释放资源
   void dispose() {
+    if (_disposed) return;
+    _disposed = true;
+    ledgerIdResolver = null;
     stopListeningRealtime();
     _eventsController.close();
   }
@@ -369,6 +373,7 @@ class SyncEngine implements app.SyncService {
 
   /// 执行完整同步（先 push 后 pull）
   Future<SyncResult> sync({required String ledgerId}) async {
+    if (_disposed) return const SyncResult(error: 'Cloud session closed');
     logger.info('SyncEngine', '开始同步 ledger=$ledgerId');
     try {
       final ledgerIdInt = int.tryParse(ledgerId) ?? -1;
@@ -532,14 +537,16 @@ class SyncEngine implements app.SyncService {
   /// 此时设备全局 cursor 可能已经前移、普通 `_pull` 再也拉不回历史。
   ///
   /// 返回新增（非已存在）的账本数，调用方可据此决定要不要 bump 刷新信号。
-  /// 并发互斥锁 — **static** 跨 SyncEngine 实例共享。
-  /// 关键 bug:join page 拿 syncEngineProvider(family) 的 engine,WS listener
-  /// 拿 cloudSyncServiceProvider 创建的 engine,两个不同 instance!instance-level
-  /// 字段互不知道,各跑各的。改 static 后整个进程同一时间只有一个 fetch-then-write
-  /// 在跑。
-  static Completer<int>? _syncLedgersInFlight;
+  /// 同一会话共用一个 engine；切换会话不能复用旧服务器的 in-flight 结果。
+  Completer<int>? _syncLedgersInFlight;
+
+  // Different engines using the same database must not interleave ledger
+  // lookup/insert/GC. Queue work, not results: a new session must fetch its own
+  // server's ledger list after the previous operation has finished.
+  static final _ledgerSyncTails = Expando<Future<void>>();
 
   Future<int> syncLedgersFromServer() async {
+    if (_disposed) throw StateError('Cloud session closed');
     final existing = _syncLedgersInFlight;
     if (existing != null) {
       logger.info('SyncEngine', 'syncLedgersFromServer 已在执行中,等待 in-flight 结果');
@@ -548,7 +555,14 @@ class SyncEngine implements app.SyncService {
     final completer = Completer<int>();
     _syncLedgersInFlight = completer;
     try {
-      final n = await _syncLedgersFromServerLocked();
+      final previous = _ledgerSyncTails[db] ?? Future<void>.value();
+      final work = previous.then((_) async {
+        if (_disposed) return 0;
+        return _syncLedgersFromServerLocked();
+      });
+      _ledgerSyncTails[db] = work.then<void>((_) {},
+          onError: (Object error, StackTrace stack) {});
+      final n = await work;
       completer.complete(n);
       return n;
     } catch (e, st) {
@@ -563,6 +577,7 @@ class SyncEngine implements app.SyncService {
     logger.info('SyncEngine', 'syncLedgersFromServer start');
     try {
       final remote = await provider.readLedgers();
+      if (_disposed) return 0;
       int upserted = 0;
       int inserted = 0;
       // 新设备登录场景:Editor 已是 server LedgerMember 但本地 ledgers 表为空。
@@ -572,6 +587,7 @@ class SyncEngine implements app.SyncService {
       // 也会让单个失败影响其它账本。
       final newSharedLedgerSyncIds = <String>[];
       for (final r in remote) {
+        if (_disposed) return inserted;
         final syncId = r.ledgerId;
         if (syncId.isEmpty) continue;
         // 用 get() 不用 getSingleOrNull() — 历史可能已经产生过同 syncId 多行
@@ -711,6 +727,7 @@ class SyncEngine implements app.SyncService {
   /// 否则单飞失效。这俩内部应该只处理 ledger-scope change(transaction / budget /
   /// ledger / ledger_snapshot)。
   Future<int> pushUserGlobalEntities() async {
+    if (_disposed) throw StateError('Cloud session closed');
     final inFlight = _userGlobalPushInFlight;
     if (inFlight != null) {
       logger.info('SyncEngine', 'pushUserGlobalEntities 已在执行,复用 in-flight');
@@ -904,6 +921,7 @@ class SyncEngine implements app.SyncService {
   /// user-global change(account / category / tag)由 [pushUserGlobalEntities] 统一推
   /// (在 [_doPush] 开头调用),避免多账本场景下并行 push 重复推送 user-global。
   Future<int> push(String ledgerId) async {
+    if (_disposed) throw StateError('Cloud session closed');
     final inFlight = _pushInFlight[ledgerId];
     if (inFlight != null) {
       logger.info('SyncEngine', 'push(ledger=$ledgerId) 已在执行,复用 in-flight');
@@ -1062,6 +1080,7 @@ class SyncEngine implements app.SyncService {
   ///   轮)
   /// - replay(sinceOverride 非 null)语义独立,等 in-flight 完成后再自己跑
   Future<int> pull(String ledgerId, {int? sinceOverride}) async {
+    if (_disposed) throw StateError('Cloud session closed');
     // 1. in-flight 单飞
     final inFlight = _pullInFlight;
     if (inFlight != null) {
@@ -1214,6 +1233,7 @@ class SyncEngine implements app.SyncService {
   /// - SQLite busy/locked → 单条 retry 2 次
   Future<_PullPageOutcome> _applyPullPage(
       List<BeeCountCloudSyncChange> changes) async {
+    if (_disposed) throw StateError('Cloud session closed');
     int applied = 0;
     int skipped = 0;
     BeeCountCloudSyncChange? failingChange;
@@ -1221,6 +1241,7 @@ class SyncEngine implements app.SyncService {
     try {
       await db.transaction(() async {
         for (final ch in changes) {
+          if (_disposed) throw StateError('Cloud session closed');
           failingChange = ch;
           final ok = await _applyOneWithBusyRetry(ch);
           if (ok) {
diff --git a/lib/cloud/sync/sync_engine_profile.dart b/lib/cloud/sync/sync_engine_profile.dart
index 2692f9bbb..779b3abf3 100644
--- a/lib/cloud/sync/sync_engine_profile.dart
+++ b/lib/cloud/sync/sync_engine_profile.dart
@@ -15,12 +15,14 @@ extension SyncEngineProfile on SyncEngine {
   /// PR 3:不再接 callback,所有字段更新走 [events] stream emit
   /// `ProfileFieldApplied` 事件,UI 通过 syncEventStreamProvider 订阅处理。
   Future<bool> syncMyProfile() async {
+    if (_disposed) return false;
     final localVersion = await AvatarService.getStoredRemoteVersion();
     logger.info('avatar_sync',
         'syncMyProfile start, localVersion=$localVersion');
     bool anyChanged = false;
     try {
       final profile = await provider.getMyProfile();
+      if (_disposed) return false;
 
       // === theme_primary_color ===
       final theme = profile.themePrimaryColor;
@@ -87,6 +89,7 @@ extension SyncEngineProfile on SyncEngine {
         userId: profile.userId,
         version: remoteVersion > 0 ? remoteVersion : null,
       );
+      if (_disposed) return false;
       logger.info('avatar_sync', 'downloaded size=${bytes.length}B');
       await AvatarService.saveAvatarFromBytes(bytes);
       await AvatarService.setStoredRemoteVersion(remoteVersion);
diff --git a/lib/cloud/sync/sync_engine_realtime.dart b/lib/cloud/sync/sync_engine_realtime.dart
index ba9bc776f..506541e4c 100644
--- a/lib/cloud/sync/sync_engine_realtime.dart
+++ b/lib/cloud/sync/sync_engine_realtime.dart
@@ -8,6 +8,7 @@ part of 'sync_engine.dart';
 extension SyncEngineRealtime on SyncEngine {
   /// 开始监听 WebSocket 实时事件，收到变更通知时自动触发 pull
   void startListeningRealtime() {
+    if (_disposed) return;
     _realtimeSubscription?.cancel();
     // 启动 WebSocket 连接，否则 realtimeEvents 流永远为空
     provider.startRealtime().catchError((e) {
@@ -66,6 +67,7 @@ extension SyncEngineRealtime on SyncEngine {
   /// 2 秒防抖：WiFi ↔ 移动网络切换、或 WS reconnect 接着 connectivity 事件
   /// 这种"连续上线信号"只触发 1 次 sync。
   void _scheduleAutoSync({required String reason}) {
+    if (_disposed) return;
     _autoSyncDebounce?.cancel();
     _autoSyncDebounce = Timer(const Duration(seconds: 2), () async {
       if (_autoSyncing) {
@@ -617,6 +619,7 @@ extension SyncEngineRealtime on SyncEngine {
 
   /// 防抖调度 pull（1 秒内多次触发只执行一次）
   void _schedulePull(String? ledgerId) {
+    if (_disposed) return;
     _pullDebounce?.cancel();
     _pullDebounce = Timer(const Duration(seconds: 1), () async {
       if (_autoPulling) return;
diff --git a/lib/cloud/sync/sync_providers.dart b/lib/cloud/sync/sync_providers.dart
index 38572a5b8..c5c36c656 100644
--- a/lib/cloud/sync/sync_providers.dart
+++ b/lib/cloud/sync/sync_providers.dart
@@ -3,6 +3,7 @@ import 'package:flutter_cloud_sync/flutter_cloud_sync.dart'
     hide SyncStatus;
 
 import '../../providers/database_providers.dart';
+import '../../providers/sync_providers.dart' show activeCloudServicesProvider;
 import 'change_tracker.dart';
 import 'sync_engine.dart';
 
@@ -23,6 +24,13 @@ final changeTrackerProvider = Provider<ChangeTracker>((ref) {
 /// 装配 callback 后才启动,但 dispose 由 Riverpod GC family entry 时统一触发。
 final syncEngineProvider = Provider.family<SyncEngine, BeeCountCloudProvider>(
   (ref, provider) {
+    // Loading with the same previous value is not a new session.
+    final session = ref.watch(activeCloudServicesProvider.select(
+        (value) => value.valueOrNull));
+    if (session == null || session.isClosed ||
+        !identical(session.services.provider, provider)) {
+      throw StateError('SyncEngine requires the active cloud session');
+    }
     final db = ref.watch(databaseProvider);
     final tracker = ref.watch(changeTrackerProvider);
     final repo = ref.watch(repositoryProvider);
@@ -32,7 +40,11 @@ final syncEngineProvider = Provider.family<SyncEngine, BeeCountCloudProvider>(
       changeTracker: tracker,
       repo: repo,
     );
-    ref.onDispose(() => engine.dispose());
+    final unregister = session.onClose(engine.dispose);
+    ref.onDispose(() {
+      unregister();
+      engine.dispose();
+    });
     return engine;
   },
 );
diff --git a/lib/cloud/transactions_sync_manager.dart b/lib/cloud/transactions_sync_manager.dart
index db30e5be5..8bb92b74b 100644
--- a/lib/cloud/transactions_sync_manager.dart
+++ b/lib/cloud/transactions_sync_manager.dart
@@ -11,6 +11,7 @@ import '../services/data_import_service.dart';
 import '../services/system/logger_service.dart';
 import 'sync_diff_service.dart';
 import 'sync_service.dart';
+import 'cloud_session_manager.dart';
 import 'transactions_json.dart';
 
 /// 账本交易的云同步管理器
@@ -20,6 +21,7 @@ class TransactionsSyncManager implements SyncService {
   final fcs.CloudServiceConfig config;
   final BeeDatabase db;
   final BaseRepository repo;
+  final CloudSession session;
 
   fcs.CloudSyncManager<int>? _syncManager;
   fcs.CloudProvider? _provider;
@@ -34,6 +36,7 @@ class TransactionsSyncManager implements SyncService {
     required this.config,
     required this.db,
     required this.repo,
+    required this.session,
   });
 
   @override
@@ -47,6 +50,7 @@ class TransactionsSyncManager implements SyncService {
 
   /// 确保服务已初始化（延迟初始化）
   Future<void> _ensureInitialized() async {
+    if (session.isClosed) throw StateError('Cloud session closed');
     if (_isInitialized) return;
     if (_isInitializing) {
       // 等待初始化完成
@@ -67,7 +71,7 @@ class TransactionsSyncManager implements SyncService {
 
   /// 初始化 CloudProvider 和 SyncManager
   Future<void> _initialize() async {
-    final services = await fcs.createCloudServices(config);
+    final services = session.services;
     _provider = services.provider;
 
     if (_provider == null) {
diff --git a/lib/pages/cloud/cloud_service_page.dart b/lib/pages/cloud/cloud_service_page.dart
index da8134b83..8a93b5bfb 100644
--- a/lib/pages/cloud/cloud_service_page.dart
+++ b/lib/pages/cloud/cloud_service_page.dart
@@ -1809,6 +1809,15 @@ class _CloudServicePageState extends ConsumerState<CloudServicePage> {
       String? errorDetail;
 
       try {
+        if (config.type == CloudBackendType.beecountCloud ||
+            config.type == CloudBackendType.s3) {
+          final active = ref.read(activeCloudServicesProvider);
+          // Retry initialization errors only. Keep healthy sessions and an
+          // already-running initialization shared with all other consumers.
+          if (active.hasError && !active.isLoading) {
+            ref.invalidate(activeCloudServicesProvider);
+          }
+        }
         switch (config.type) {
           case CloudBackendType.local:
             break;
@@ -1883,14 +1892,15 @@ class _CloudServicePageState extends ConsumerState<CloudServicePage> {
             break;
 
           case CloudBackendType.beecountCloud:
-            // BeeCount Cloud 连接测试 - 调用健康检查接口
+            // 已激活服务的认证与连接测试共用会话。
             try {
-              final services = await createCloudServices(config);
-              if (services.provider == null) {
+              final session = await ref.read(activeCloudServicesProvider.future);
+              final provider = session.services.provider;
+              if (provider == null) {
                 throw Exception('BeeCount Cloud provider 初始化失败');
               }
               // 尝试列出文件验证连接
-              await services.provider!.storage.list(path: '');
+              await provider.storage.list(path: '');
               connectionSuccess = true;
             } catch (e) {
               String errorMsg = e.toString();
@@ -1919,7 +1929,8 @@ class _CloudServicePageState extends ConsumerState<CloudServicePage> {
 
               logger.info('CloudServicePage', 'S3 连接测试开始: endpoint=${cleanedConfig.s3Endpoint}, bucket=${cleanedConfig.s3Bucket}');
 
-              final services = await createCloudServices(cleanedConfig);
+              final session = await ref.read(activeCloudServicesProvider.future);
+              final services = session.services;
 
               logger.info('CloudServicePage', 'S3 provider 创建结果: ${services.provider != null ? "成功" : "失败"}');
 
diff --git a/lib/pages/cloud/devices_page.dart b/lib/pages/cloud/devices_page.dart
index 7d1923949..8a54360bd 100644
--- a/lib/pages/cloud/devices_page.dart
+++ b/lib/pages/cloud/devices_page.dart
@@ -82,17 +82,12 @@ class _DevicesPageState extends ConsumerState<DevicesPage> {
 
   /// 获取 BeeCountCloudProvider 实例（仅 beecountCloud 后端可用）
   Future<BeeCountCloudProvider> _getCloudProvider() async {
-    final config = await ref.read(activeCloudConfigProvider.future);
-    if (!config.valid || config.type != CloudBackendType.beecountCloud) {
-      throw StateError(
-          AppLocalizations.of(context).cloudCollabUnavailableMessage);
+    final unavailable = AppLocalizations.of(context).cloudCollabUnavailableMessage;
+    final provider = await ref.read(beecountCloudProviderInstance.future);
+    if (provider == null) {
+      throw StateError(unavailable);
     }
-    final services = await createCloudServices(config);
-    if (services.provider == null || services.provider is! BeeCountCloudProvider) {
-      throw StateError(
-          AppLocalizations.of(context).cloudCollabUnavailableMessage);
-    }
-    return services.provider as BeeCountCloudProvider;
+    return provider;
   }
 
   Future<void> _reload({bool keepLoadingState = true}) async {
diff --git a/lib/providers/sync_providers.dart b/lib/providers/sync_providers.dart
index 0dd78abe2..7f5696d31 100644
--- a/lib/providers/sync_providers.dart
+++ b/lib/providers/sync_providers.dart
@@ -9,6 +9,7 @@ import 'package:flutter_riverpod/flutter_riverpod.dart';
 import 'package:shared_preferences/shared_preferences.dart';
 import 'package:flutter_cloud_sync/flutter_cloud_sync.dart' hide SyncStatus;
 import '../cloud/sync_service.dart';
+import '../cloud/cloud_session_manager.dart';
 import 'shared_ledger_providers.dart';
 import '../cloud/sync/sync_coordinator.dart';
 import '../cloud/sync/sync_engine.dart';
@@ -144,27 +145,26 @@ final s3ConfigProvider = FutureProvider<CloudServiceConfig?>((ref) async {
   return store.loadS3();
 });
 
-final authServiceProvider = FutureProvider<CloudAuthService>((ref) async {
-  final activeAsync = ref.watch(activeCloudConfigProvider);
-  if (!activeAsync.hasValue) {
-    return NoopAuthService();
-  }
-
-  final config = activeAsync.value!;
-  if (!config.valid || config.type == CloudBackendType.local) {
-    return NoopAuthService();
-  }
+/// Owns services across projection rebuilds and configuration switches.
+final cloudSessionManagerProvider = Provider<CloudSessionManager>((ref) {
+  final manager = CloudSessionManager();
+  ref.onDispose(() => unawaited(manager.dispose().catchError(
+      (Object e, StackTrace st) => logger.warning('CloudSession', 'Dispose failed: $e', st))));
+  return manager;
+});
 
-  try {
-    final services = await createCloudServices(config);
-    if (services.auth != null) {
-      return services.auth!;
-    }
-  } catch (e) {
-    // 初始化失败，返回 NoopAuthService
-  }
+final activeCloudServicesProvider = FutureProvider<CloudSession>((ref) async {
+  final manager = ref.watch(cloudSessionManagerProvider);
+  var cancelled = false;
+  ref.onDispose(() => cancelled = true);
+  final config = await ref.watch(activeCloudConfigProvider.future);
+  if (cancelled) throw StateError('Cloud configuration changed');
+  return manager.activate(config);
+});
 
-  return NoopAuthService();
+final authServiceProvider = FutureProvider<CloudAuthService>((ref) async {
+  final session = await ref.watch(activeCloudServicesProvider.future);
+  return session.services.auth ?? NoopAuthService();
 });
 
 // 防重入锁：避免 Provider 重建导致多个自动同步并发执行
@@ -172,7 +172,7 @@ bool _autoSyncInProgress = false;
 
 final syncServiceProvider = Provider<SyncService>((ref) {
   final activeAsync = ref.watch(activeCloudConfigProvider);
-  if (!activeAsync.hasValue) return LocalOnlySyncService();
+  if (activeAsync.isLoading || !activeAsync.hasValue) return LocalOnlySyncService();
 
   final config = activeAsync.value!;
   if (!config.valid || config.type == CloudBackendType.local) {
@@ -182,7 +182,7 @@ final syncServiceProvider = Provider<SyncService>((ref) {
   // BeeCount Cloud → SyncEngine（增量同步）
   if (config.type == CloudBackendType.beecountCloud) {
     final providerAsync = ref.watch(beecountCloudProviderInstance);
-    if (!providerAsync.hasValue || providerAsync.value == null) {
+    if (providerAsync.isLoading || !providerAsync.hasValue || providerAsync.value == null) {
       // Provider 尚未初始化，返回 LocalOnly 等待
       return LocalOnlySyncService();
     }
@@ -485,60 +485,21 @@ final syncServiceProvider = Provider<SyncService>((ref) {
   // 其他 provider → TransactionsSyncManager（快照同步）
   final db = ref.watch(databaseProvider);
   final repo = ref.watch(repositoryProvider);
-  return TransactionsSyncManager(config: config, db: db, repo: repo);
+  final servicesAsync = ref.watch(activeCloudServicesProvider);
+  if (servicesAsync.isLoading) return LocalOnlySyncService();
+  final session = servicesAsync.valueOrNull;
+  if (session == null || session.isClosed) return LocalOnlySyncService();
+  return TransactionsSyncManager(config: config, db: db, repo: repo,
+      session: session);
 });
 
 /// 已初始化的 BeeCountCloudProvider 实例
 /// 用于 SyncEngine 和其他需要直接访问 BeeCount Cloud API 的场景
 final beecountCloudProviderInstance =
     FutureProvider<BeeCountCloudProvider?>((ref) async {
-  final configAsync = ref.watch(activeCloudConfigProvider);
-  if (!configAsync.hasValue) return null;
-
-  final config = configAsync.value!;
-  if (!config.valid || config.type != CloudBackendType.beecountCloud) {
-    return null;
-  }
-
-  try {
-    final services = await createCloudServices(config);
-    if (services.provider is! BeeCountCloudProvider) return null;
-    final provider = services.provider as BeeCountCloudProvider;
-
-    final email = config.beecountCloudEmail;
-    final password = config.beecountCloudPassword;
-
-    // 把邮密交给 auth service,让它在任何时刻发现 session 失效都能自动重登。
-    // 这是解决"token 过期后必须到配置页点一下才能恢复"的关键:auth service
-    // 内部会在 currentUser / requireAccessToken 触发时尝试恢复,不再等 Provider
-    // 重建。
-    if (services.auth is BeeCountCloudAuthService) {
-      (services.auth as BeeCountCloudAuthService).setRecoveryCredentials(
-        email: email,
-        password: password,
-      );
-    }
-
-    // 双重保险:构造之后也触发一次 currentUser,让 initialize() 没恢复出
-    // session 的场景立刻走一次恢复登录(email+password 有时),减少用户第一次
-    // 操作时的卡顿感。currentUser 内部已经自带 _tryRecoveryLogin。
-    if (services.auth != null) {
-      try {
-        final user = await services.auth!.currentUser;
-        if (user != null) {
-          logger.info('CloudSync', 'BeeCount Cloud session ready: ${user.email}');
-        } else if (email != null && email.isNotEmpty) {
-          logger.info('CloudSync', 'BeeCount Cloud 未登录,等首次 API 触发恢复');
-        }
-      } catch (e, st) {
-        logger.warning('CloudSync', 'BeeCount Cloud 初始 currentUser 失败: $e', st);
-      }
-    }
-    return provider;
-  } catch (e, st) {
-    logger.error('CloudSync', 'BeeCountCloudProvider 初始化失败', e, st);
-  }
-  return null;
+  final session = await ref.watch(activeCloudServicesProvider.future);
+  final provider = session.services.provider;
+  return provider is BeeCountCloudProvider ? provider : null;
 });
 
 /// BeeCount Cloud 服务端版本号。Mine 页面 / 云同步页都能直接用;失败就
diff --git a/packages/flutter_cloud_sync/lib/src/config/provider_factory.dart b/packages/flutter_cloud_sync/lib/src/config/provider_factory.dart
index e0c2a0f1f..0c5388acf 100644
--- a/packages/flutter_cloud_sync/lib/src/config/provider_factory.dart
+++ b/packages/flutter_cloud_sync/lib/src/config/provider_factory.dart
@@ -19,8 +19,9 @@ import 'cloud_service_config.dart';
 /// - Supabase: 使用独立包内的初始化逻辑
 /// - WebDAV: 创建新的 WebDAV provider
 Future<({CloudProvider? provider, CloudAuthService? auth})> createCloudServices(
-  CloudServiceConfig config,
-) async {
+  CloudServiceConfig config, {
+  bool persistSession = true,
+}) async {
   if (!config.valid) {
     return (provider: null, auth: null);
   }
@@ -34,6 +35,8 @@ Future<({CloudProvider? provider, CloudAuthService? auth})> createCloudServices(
       await provider.initialize({
         'baseUrl': config.beecountCloudBaseUrl!,
         'apiPrefix': config.beecountCloudApiPrefix ?? '/api/v1',
+        'persistSession': persistSession,
+        'email': config.beecountCloudEmail,
       });
       return (provider: provider, auth: provider.auth);
 
@@ -88,7 +91,7 @@ Future<({CloudProvider? provider, CloudAuthService? auth})> createCloudServices(
       // S3 初始化 - 不捕获异常，让错误向上传递以便调试
       final provider = S3Provider();
       await provider.initialize({
-        'endpoint': config.s3Endpoint!,
+        'endpoint': config.s3Endpoint!.replaceFirst(RegExp(r'^https?://'), ''),
         'region': config.s3Region ?? 'us-east-1',
         'accessKey': config.s3AccessKey!,
         'secretKey': config.s3SecretKey!,
diff --git a/packages/flutter_cloud_sync/lib/src/providers/beecount_cloud_provider.dart b/packages/flutter_cloud_sync/lib/src/providers/beecount_cloud_provider.dart
index 8856906cf..74c63c82e 100644
--- a/packages/flutter_cloud_sync/lib/src/providers/beecount_cloud_provider.dart
+++ b/packages/flutter_cloud_sync/lib/src/providers/beecount_cloud_provider.dart
@@ -126,8 +126,9 @@ class BeeCountCloudProvider implements CloudProvider {
       baseUrl: baseUrl,
       apiPrefix: apiPrefix,
       twoFactorHandler: BeeCountCloudProvider.globalTwoFactorHandler,
+      persistSession: config['persistSession'] != false,
     );
-    await authService.initialize();
+    await authService.initialize(expectedEmail: config['email'] as String?);
 
     _auth = authService;
     final storage = BeeCountCloudStorageService(
@@ -1119,6 +1120,7 @@ class BeeCountCloudAuthService implements CloudAuthService {
     required this.apiPrefix,
     http.Client? httpClient,
     TwoFactorChallengeHandler? twoFactorHandler,
+    this.persistSession = true,
   })  : _httpClient = httpClient ?? http.Client(),
         _twoFactorHandler = twoFactorHandler;
 
@@ -1126,6 +1128,8 @@ class BeeCountCloudAuthService implements CloudAuthService {
   final String apiPrefix;
   final http.Client _httpClient;
   final TwoFactorChallengeHandler? _twoFactorHandler;
+  final bool persistSession;
+  bool _disposed = false;
 
   final StreamController<CloudUser?> _authStateController =
       StreamController<CloudUser?>.broadcast();
@@ -1174,7 +1178,8 @@ class BeeCountCloudAuthService implements CloudAuthService {
     return 'beecount_cloud_local_device_id_$digest';
   }
 
-  Future<void> initialize() async {
+  Future<void> initialize({String? expectedEmail}) async {
+    if (!persistSession) return;
     final prefs = await SharedPreferences.getInstance();
     final raw = prefs.getString(_sessionStorageKey);
     if (raw == null || raw.isEmpty) {
@@ -1183,7 +1188,11 @@ class BeeCountCloudAuthService implements CloudAuthService {
 
     try {
       final json = jsonDecode(raw) as Map<String, dynamic>;
-      _session = _BeeCountCloudSession.fromJson(json);
+      final saved = _BeeCountCloudSession.fromJson(json);
+      final email = expectedEmail?.trim().toLowerCase();
+      if (email != null && email.isNotEmpty &&
+          saved.email?.trim().toLowerCase() != email) return;
+      _session = saved;
       if (_isAccessTokenExpired(_session!)) {
         await _refreshSessionOrClear();
       } else {
@@ -1199,6 +1208,7 @@ class BeeCountCloudAuthService implements CloudAuthService {
 
   @override
   Future<CloudUser?> get currentUser async {
+    if (_disposed) return null;
     final session = _session;
     if (session == null) {
       // 完全没 session(从没登过 / session 被清了):只有带了恢复凭证才尝试
@@ -1218,6 +1228,7 @@ class BeeCountCloudAuthService implements CloudAuthService {
   }
 
   Future<String> requireAccessToken() async {
+    if (_disposed) throw CloudNotAuthenticatedException('Cloud session closed');
     final session = _session;
     if (session == null) {
       final recovered = await _tryRecoveryLogin();
@@ -1495,6 +1506,7 @@ class BeeCountCloudAuthService implements CloudAuthService {
   }
 
   Future<String> _resolveOrCreateLocalDeviceId() async {
+    if (!persistSession) return _generateLocalDeviceId();
     final prefs = await SharedPreferences.getInstance();
     final existing = _trimOrNull(prefs.getString(_localDeviceIdStorageKey));
     if (existing != null) {
@@ -1594,6 +1606,8 @@ class BeeCountCloudAuthService implements CloudAuthService {
   }
 
   void dispose() {
+    if (_disposed) return;
+    _disposed = true;
     _authStateController.close();
     _httpClient.close();
   }
@@ -1746,12 +1760,16 @@ class BeeCountCloudAuthService implements CloudAuthService {
   }
 
   Future<void> _saveSession(_BeeCountCloudSession session) async {
+    if (_disposed) throw CloudNotAuthenticatedException('Cloud session closed');
     _session = session;
     // 任何成功登录路径都清掉静默恢复冷却,避免之前的失败状态拖到现在。
     _silentRecoveryCooldownUntil = null;
-    final prefs = await SharedPreferences.getInstance();
-    await prefs.setString(_sessionStorageKey, jsonEncode(session.toJson()));
-    await prefs.setString(_localDeviceIdStorageKey, session.deviceId);
+    if (persistSession) {
+      final prefs = await SharedPreferences.getInstance();
+      if (_disposed) throw CloudNotAuthenticatedException('Cloud session closed');
+      await prefs.setString(_sessionStorageKey, jsonEncode(session.toJson()));
+      await prefs.setString(_localDeviceIdStorageKey, session.deviceId);
+    }
     final metadata = _deviceMetadataCache;
     if (metadata != null && metadata.deviceId != session.deviceId) {
       _deviceMetadataCache = _BeeCountDeviceMetadata(
@@ -1767,13 +1785,17 @@ class BeeCountCloudAuthService implements CloudAuthService {
   }
 
   Future<void> _clearSession() async {
+    if (_disposed) return;
     _session = null;
-    final prefs = await SharedPreferences.getInstance();
-    await prefs.remove(_sessionStorageKey);
-    _authStateController.add(null);
+    if (persistSession) {
+      final prefs = await SharedPreferences.getInstance();
+      await prefs.remove(_sessionStorageKey);
+    }
+    if (!_disposed) _authStateController.add(null);
   }
 
   void _emitCurrentUser() {
+    if (_disposed) return;
     final session = _session;
     if (session == null) {
       _authStateController.add(null);
@@ -1805,6 +1827,7 @@ class BeeCountCloudAuthService implements CloudAuthService {
     Map<String, dynamic>? body,
     String? accessToken,
   }) async {
+    if (_disposed) throw CloudNotAuthenticatedException('Cloud session closed');
     final uri = Uri.parse('$baseUrl$apiPrefix$path');
     final request = http.Request(method, uri);
     request.headers['Content-Type'] = 'application/json';
diff --git a/test/cloud/cloud_session_manager_test.dart b/test/cloud/cloud_session_manager_test.dart
new file mode 100644
index 000000000..9c8aba24d
--- /dev/null
+++ b/test/cloud/cloud_session_manager_test.dart
@@ -0,0 +1,160 @@
+import 'dart:async';
+
+import 'package:flutter_cloud_sync/flutter_cloud_sync.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:shared_preferences/shared_preferences.dart';
+import 'package:beecount/cloud/cloud_session_manager.dart';
+
+import 'sync/_fakes/fake_beecount_cloud_provider.dart';
+
+const configA = CloudServiceConfig(
+    type: CloudBackendType.beecountCloud,
+    name: 'A',
+    beecountCloudBaseUrl: 'https://a.example');
+const configB = CloudServiceConfig(
+    type: CloudBackendType.beecountCloud,
+    name: 'B',
+    beecountCloudBaseUrl: 'https://b.example');
+
+class TrackedProvider extends FakeBeeCountCloudProvider {
+  int closed = 0;
+  @override
+  Future<void> dispose() async {
+    closed++;
+  }
+}
+
+void main() {
+  TestWidgetsFlutterBinding.ensureInitialized();
+  setUp(() => SharedPreferences.setMockInitialValues({}));
+
+  test('concurrent consumers and equal reloaded configurations share services',
+      () async {
+    var creates = 0;
+    final provider = TrackedProvider();
+    final manager = CloudSessionManager(factory: (_) async {
+      creates++;
+      return (provider: provider, auth: provider.auth);
+    });
+    final sessions = await Future.wait([
+      manager.activate(configA),
+      manager.activate(configA),
+      manager.activate(CloudServiceConfig.fromJson(configA.toJson())),
+    ]);
+    expect(creates, 1);
+    expect(sessions.every((s) => identical(s, sessions.first)), isTrue);
+    await manager.dispose();
+    await manager.dispose();
+    expect(provider.closed, 1);
+  });
+
+  test(
+      'switch stops consumers and releases old services before creating new ones',
+      () async {
+    final events = <String>[];
+    final first = TrackedProvider();
+    final second = TrackedProvider();
+    final manager = CloudSessionManager(factory: (cfg) async {
+      if (cfg == configB) {
+        expect(first.closed, 1);
+        expect(events, ['stop engine']);
+      }
+      final p = cfg == configA ? first : second;
+      return (provider: p, auth: p.auth);
+    });
+    final old = await manager.activate(configA);
+    old.onClose(() => events.add('stop engine'));
+    await manager.activate(configB);
+    expect(old.isClosed, isTrue);
+    await manager.dispose();
+    expect(second.closed, 1);
+  });
+
+  test(
+      'late initialization from superseded config is disposed, never published',
+      () async {
+    final started = Completer<void>();
+    final release = Completer<void>();
+    final first = TrackedProvider();
+    final second = TrackedProvider();
+    final manager = CloudSessionManager(factory: (cfg) async {
+      if (cfg == configA) {
+        started.complete();
+        await release.future;
+      }
+      final p = cfg == configA ? first : second;
+      return (provider: p, auth: p.auth);
+    });
+    final obsolete = manager.activate(configA);
+    final rejected = expectLater(obsolete, throwsStateError);
+    await started.future;
+    final current = manager.activate(configB);
+    release.complete();
+    await rejected;
+    expect((await current).services.provider, second);
+    expect(first.closed, 1);
+    await manager.dispose();
+  });
+
+  test('failed initialization can retry the same configuration', () async {
+    var attempts = 0;
+    final p = TrackedProvider();
+    final manager = CloudSessionManager(factory: (_) async {
+      if (++attempts == 1) throw StateError('offline');
+      return (provider: p, auth: p.auth);
+    });
+    await expectLater(manager.activate(configA), throwsStateError);
+    expect((await manager.activate(configA)).services.provider, p);
+    await manager.dispose();
+  });
+
+  test('a failing close listener does not skip remaining cleanup', () async {
+    final provider = TrackedProvider();
+    final session = CloudSession(configA,
+        (provider: provider, auth: provider.auth));
+    var stopped = false;
+    session.onClose(() => throw StateError('listener failed'));
+    session.onClose(() => stopped = true);
+    await expectLater(session.close(), throwsStateError);
+    expect(stopped, isTrue);
+    expect(provider.closed, 1);
+  });
+
+  test('shutdown during creation disposes late services', () async {
+    final started = Completer<void>();
+    final release = Completer<void>();
+    final p = TrackedProvider();
+    final manager = CloudSessionManager(factory: (_) async {
+      started.complete();
+      await release.future;
+      return (provider: p, auth: p.auth);
+    });
+    final pending = expectLater(manager.activate(configA), throwsStateError);
+    await started.future;
+    final closing = manager.dispose();
+    release.complete();
+    await pending;
+    await closing;
+    expect(p.closed, 1);
+  });
+
+  test('temporary failure releases draft without replacing active services',
+      () async {
+    final p = TrackedProvider();
+    final draft = TrackedProvider();
+    final manager = CloudSessionManager(
+      factory: (_) async => (provider: p, auth: p.auth),
+      temporaryFactory: (_) async => (provider: draft, auth: draft.auth),
+    );
+    final active = await manager.activate(configA);
+    await expectLater(
+        manager.withTemporarySession<void>(configB, (_) async {
+          throw StateError('test failed');
+        }),
+        throwsStateError);
+    expect(draft.closed, 1);
+    expect(p.closed, 0);
+    expect(await manager.activate(configA), same(active));
+    await manager.dispose();
+  });
+}
diff --git a/test/cloud/sync/_fakes/fake_beecount_cloud_provider.dart b/test/cloud/sync/_fakes/fake_beecount_cloud_provider.dart
index 2c69ac8f9..e93779489 100644
--- a/test/cloud/sync/_fakes/fake_beecount_cloud_provider.dart
+++ b/test/cloud/sync/_fakes/fake_beecount_cloud_provider.dart
@@ -60,6 +60,7 @@ class FakeBeeCountCloudAuthService extends BeeCountCloudAuthService {
 class FakeBeeCountCloudStorageService implements CloudStorageService {
   final Map<String, String> _files = {};
   final Map<String, Map<String, String>?> _metadata = {};
+  int listCallCount = 0;
 
   /// 测试 helper:模拟 server 端账本列表(`storage.list(path: '')` 返回)
   final List<CloudFile> ledgerSnapshots = [];
@@ -88,6 +89,7 @@ class FakeBeeCountCloudStorageService implements CloudStorageService {
 
   @override
   Future<List<CloudFile>> list({required String path}) async {
+    listCallCount++;
     // 测试关注的是"远端账本列表",由 [ledgerSnapshots] 控制
     return List.unmodifiable(ledgerSnapshots);
   }
@@ -147,6 +149,8 @@ class FakeBeeCountCloudProvider extends BeeCountCloudProvider {
   /// 控制 storage.list 是否抛错
   Exception? storageListError;
 
+  int get storageListCallCount => _fakeStorage.listCallCount;
+
   final StreamController<BeeCountCloudRealtimeEvent> _realtimeController =
       StreamController<BeeCountCloudRealtimeEvent>.broadcast();
 
diff --git a/test/cloud/sync/sync_engine_session_queue_test.dart b/test/cloud/sync/sync_engine_session_queue_test.dart
new file mode 100644
index 000000000..90fa16e7f
--- /dev/null
+++ b/test/cloud/sync/sync_engine_session_queue_test.dart
@@ -0,0 +1,62 @@
+import 'dart:async';
+
+import 'package:beecount/cloud/sync/change_tracker.dart';
+import 'package:beecount/cloud/sync/sync_engine.dart';
+import 'package:beecount/data/db.dart';
+import 'package:beecount/data/repositories/local/local_repository.dart';
+import 'package:drift/native.dart';
+import 'package:flutter_cloud_sync/flutter_cloud_sync.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:shared_preferences/shared_preferences.dart';
+
+import '_fakes/fake_beecount_cloud_provider.dart';
+
+class GatedProvider extends FakeBeeCountCloudProvider {
+  final started = Completer<void>();
+  final release = Completer<void>();
+  int calls = 0;
+
+  @override
+  Future<List<BeeCountCloudReadLedger>> readLedgers() async {
+    calls++;
+    started.complete();
+    await release.future;
+    return super.readLedgers();
+  }
+}
+
+void main() {
+  TestWidgetsFlutterBinding.ensureInitialized();
+
+  test('replacement engine waits but fetches its own server result', () async {
+    SharedPreferences.setMockInitialValues({});
+    final db = BeeDatabase.forTesting(NativeDatabase.memory());
+    final first = GatedProvider();
+    final second = GatedProvider();
+    SyncEngine makeEngine(GatedProvider provider) => SyncEngine(
+          db: db,
+          provider: provider,
+          changeTracker: ChangeTracker(db),
+          repo: LocalRepository(db),
+        );
+    final oldEngine = makeEngine(first);
+    final newEngine = makeEngine(second);
+    addTearDown(() async {
+      oldEngine.dispose();
+      newEngine.dispose();
+      await db.close();
+    });
+    final oldWork = oldEngine.syncLedgersFromServer();
+    await first.started.future;
+    oldEngine.dispose();
+    final newWork = newEngine.syncLedgersFromServer();
+    await Future<void>.delayed(Duration.zero);
+    expect(second.calls, 0);
+    first.release.complete();
+    await oldWork;
+    await second.started.future;
+    expect(second.calls, 1);
+    second.release.complete();
+    await newWork;
+  });
+}
diff --git a/test/pages/cloud/cloud_service_page_test.dart b/test/pages/cloud/cloud_service_page_test.dart
new file mode 100644
index 000000000..cad9fdc8f
--- /dev/null
+++ b/test/pages/cloud/cloud_service_page_test.dart
@@ -0,0 +1,112 @@
+import 'package:flutter/material.dart';
+import 'package:flutter_cloud_sync/flutter_cloud_sync.dart';
+import 'package:flutter_riverpod/flutter_riverpod.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:shared_preferences/shared_preferences.dart';
+
+import 'package:beecount/l10n/app_localizations.dart';
+import 'package:beecount/cloud/cloud_session_manager.dart';
+import 'package:beecount/pages/cloud/cloud_service_page.dart';
+import 'package:beecount/providers/sync_providers.dart';
+
+import '../../cloud/sync/_fakes/fake_beecount_cloud_provider.dart';
+
+void main() {
+  TestWidgetsFlutterBinding.ensureInitialized();
+
+  setUp(() {
+    SharedPreferences.setMockInitialValues({'multi_device_sync': false});
+  });
+
+  testWidgets('BeeCount Cloud 测试连接复用主 provider', (tester) async {
+    const config = CloudServiceConfig(
+      type: CloudBackendType.beecountCloud,
+      name: 'BeeCount Cloud',
+      beecountCloudBaseUrl: 'https://cloud.example.com',
+      beecountCloudApiPrefix: '/api/v1',
+    );
+    final fakeProvider = FakeBeeCountCloudProvider();
+
+    await tester.pumpWidget(
+      ProviderScope(
+        overrides: [
+          activeCloudConfigProvider.overrideWith((ref) async => config),
+          beecountCloudConfigProvider.overrideWith((ref) async => config),
+          webdavConfigProvider.overrideWith((ref) async => null),
+          s3ConfigProvider.overrideWith((ref) async => null),
+          activeCloudServicesProvider.overrideWith((ref) async => CloudSession(
+              config, (provider: fakeProvider, auth: fakeProvider.auth))),
+        ],
+        child: MaterialApp(
+          localizationsDelegates: AppLocalizations.localizationsDelegates,
+          supportedLocales: AppLocalizations.supportedLocales,
+          locale: const Locale('zh'),
+          home: const CloudServicePage(),
+        ),
+      ),
+    );
+    await tester.pumpAndSettle();
+
+    await tester.tap(find.byIcon(Icons.wifi_find));
+    await tester.pump();
+    await tester.pump(const Duration(milliseconds: 300));
+
+    expect(fakeProvider.storageListCallCount, 1);
+
+    await tester.tap(find.text('确定'));
+    await tester.pumpAndSettle();
+  });
+
+  testWidgets('S3 connection test retries failed initialization once',
+      (tester) async {
+    const config = CloudServiceConfig(
+      type: CloudBackendType.s3,
+      name: 'S3',
+      s3Endpoint: 's3.example.com',
+      s3AccessKey: 'test',
+      s3SecretKey: 'test',
+      s3Bucket: 'test',
+    );
+    final fake = FakeBeeCountCloudProvider();
+    var attempts = 0;
+    final manager = CloudSessionManager(factory: (_) async {
+      if (++attempts == 1) throw StateError('offline');
+      return (provider: fake, auth: fake.auth);
+    });
+    final container = ProviderContainer(overrides: [
+      cloudSessionManagerProvider.overrideWithValue(manager),
+      activeCloudConfigProvider.overrideWith((ref) async => config),
+      s3ConfigProvider.overrideWith((ref) async => config),
+      beecountCloudConfigProvider.overrideWith((ref) async => null),
+      webdavConfigProvider.overrideWith((ref) async => null),
+    ]);
+    await expectLater(container.read(activeCloudServicesProvider.future),
+        throwsStateError);
+    await tester.pumpWidget(UncontrolledProviderScope(
+      container: container,
+      child: MaterialApp(
+        localizationsDelegates: AppLocalizations.localizationsDelegates,
+        supportedLocales: AppLocalizations.supportedLocales,
+        locale: const Locale('zh'),
+        home: const CloudServicePage(),
+      ),
+    ));
+    await tester.pumpAndSettle();
+    for (var i = 0; i < 2; i++) {
+      await tester.tap(find.byIcon(Icons.wifi_find));
+      await tester.pump();
+      await tester.pump(const Duration(milliseconds: 300));
+      expect(attempts, 2);
+      expect(fake.storageListCallCount, i + 1);
+      await tester.tap(find.text('确定'));
+      await tester.pumpAndSettle();
+    }
+    await tester.pumpWidget(const SizedBox());
+    // Flush the logger's delayed write timer before fake-async teardown.
+    await tester.pump(const Duration(seconds: 3));
+    container.dispose();
+    final closing = manager.dispose();
+    await tester.pumpAndSettle();
+    await closing;
+  });
+}
diff --git a/test/providers/beecount_cloud_auth_provider_test.dart b/test/providers/beecount_cloud_auth_provider_test.dart
new file mode 100644
index 000000000..38e22373c
--- /dev/null
+++ b/test/providers/beecount_cloud_auth_provider_test.dart
@@ -0,0 +1,45 @@
+import 'package:flutter_cloud_sync/flutter_cloud_sync.dart';
+import 'package:flutter_riverpod/flutter_riverpod.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:shared_preferences/shared_preferences.dart';
+
+import 'package:beecount/providers/sync_providers.dart';
+
+void main() {
+  TestWidgetsFlutterBinding.ensureInitialized();
+
+  setUp(() {
+    SharedPreferences.setMockInitialValues({});
+  });
+
+  test('BeeCount Cloud UI auth and SyncEngine share one auth instance',
+      () async {
+    const config = CloudServiceConfig(
+      type: CloudBackendType.beecountCloud,
+      name: 'BeeCount Cloud',
+      beecountCloudBaseUrl: 'https://cloud.example.com',
+      beecountCloudApiPrefix: '/api/v1',
+    );
+    final container = ProviderContainer(
+      overrides: [
+        activeCloudConfigProvider.overrideWith((ref) async => config),
+      ],
+    );
+    addTearDown(container.dispose);
+
+    // 真机上 Mine/云服务页会先 watch UI auth，同步引擎随后
+    // eager-load provider。主线在这个顺序下会各自创建一套 auth。
+    final authFuture = container.read(authServiceProvider.future);
+    final providerFuture = container.read(beecountCloudProviderInstance.future);
+
+    final auth = await authFuture;
+    final provider = await providerFuture;
+
+    expect(provider, isNotNull);
+    expect(
+      identical(auth, provider!.auth),
+      isTrue,
+      reason: 'UI 与同步引擎不应持有两套独立 session',
+    );
+  });
+}
diff --git a/test/providers/cloud_session_auth_test.dart b/test/providers/cloud_session_auth_test.dart
new file mode 100644
index 000000000..fc869e502
--- /dev/null
+++ b/test/providers/cloud_session_auth_test.dart
@@ -0,0 +1,122 @@
+import 'dart:convert';
+
+import 'package:beecount/cloud/cloud_session_manager.dart';
+import 'package:beecount/providers/sync_providers.dart';
+import 'package:flutter_cloud_sync/flutter_cloud_sync.dart';
+import 'package:flutter_riverpod/flutter_riverpod.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:http/http.dart' as http;
+import 'package:http/testing.dart';
+import 'package:shared_preferences/shared_preferences.dart';
+import 'package:package_info_plus/package_info_plus.dart';
+
+import '../cloud/sync/_fakes/fake_beecount_cloud_provider.dart';
+
+class AuthProvider extends FakeBeeCountCloudProvider {
+  AuthProvider(this.sessionAuth);
+  final BeeCountCloudAuthService sessionAuth;
+  @override
+  CloudAuthService get auth => sessionAuth;
+  @override
+  Future<void> dispose() async => sessionAuth.dispose();
+}
+
+void main() {
+  TestWidgetsFlutterBinding.ensureInitialized();
+  setUp(() {
+    SharedPreferences.setMockInitialValues({});
+    PackageInfo.setMockInitialValues(
+        appName: 'test',
+        packageName: 'test',
+        version: '1',
+        buildNumber: '1',
+        buildSignature: 'test');
+  });
+
+  Map<String, dynamic> tokens(String user) => {
+        'user': {'id': user, 'email': '$user@example.com'},
+        'access_token': 'test-access',
+        'refresh_token': 'test-refresh',
+        'expires_in': 3600,
+        'device_id': 'test-device',
+      };
+
+  test('UI initialized before 2FA sees login immediately without invalidation',
+      () async {
+    final requests = <String>[];
+    final auth = BeeCountCloudAuthService(
+      baseUrl: 'https://cloud.example',
+      apiPrefix: '/api/v1',
+      httpClient: MockClient((request) async {
+        requests.add(request.url.path);
+        return http.Response(
+            jsonEncode(request.url.path.endsWith('/login')
+                ? {'requires_2fa': true, 'challenge_token': 'test-challenge'}
+                : tokens('owner')),
+            200);
+      }),
+      twoFactorHandler: (challenge) async =>
+          await challenge.verify('totp', '123456') == null,
+    );
+    final provider = AuthProvider(auth);
+    final manager = CloudSessionManager(
+        factory: (_) async => (provider: provider, auth: auth));
+    final container = ProviderContainer(overrides: [
+      cloudSessionManagerProvider.overrideWithValue(manager),
+      activeCloudConfigProvider.overrideWith((ref) async =>
+          const CloudServiceConfig(
+              type: CloudBackendType.beecountCloud,
+              name: 'test',
+              beecountCloudBaseUrl: 'https://cloud.example')),
+    ]);
+    addTearDown(() async {
+      container.dispose();
+      await manager.dispose();
+    });
+    final uiAuth = await container.read(authServiceProvider.future);
+    expect(await uiAuth.currentUser, isNull);
+    final cloud = await container.read(beecountCloudProviderInstance.future);
+    await cloud!.auth
+        .signInWithEmail(email: 'owner@example.com', password: 'test');
+    expect((await uiAuth.currentUser)?.id, 'owner');
+    container.invalidate(authServiceProvider);
+    container.invalidate(beecountCloudProviderInstance);
+    final rebuilt = await container.read(authServiceProvider.future);
+    expect((await rebuilt.currentUser)?.id, 'owner');
+    expect(requests, ['/api/v1/auth/login', '/api/v1/auth/2fa/verify']);
+  });
+
+  test('temporary BeeCount auth neither reads nor overwrites persisted session',
+      () async {
+    BeeCountCloudAuthService makeAuth(bool persist, String user) =>
+        BeeCountCloudAuthService(
+          baseUrl: 'https://cloud.example',
+          apiPrefix: '/api/v1',
+          persistSession: persist,
+          httpClient: MockClient(
+              (_) async => http.Response(jsonEncode(tokens(user)), 200)),
+        );
+    final active = makeAuth(true, 'owner');
+    final draft = makeAuth(false, 'draft');
+    addTearDown(active.dispose);
+    addTearDown(draft.dispose);
+    await active.signInWithEmail(email: 'owner@example.com', password: 'test');
+    final prefs = await SharedPreferences.getInstance();
+    final before = {for (final key in prefs.getKeys()) key: prefs.get(key)};
+    await draft.initialize();
+    expect(await draft.currentUser, isNull);
+    await draft.signInWithEmail(email: 'draft@example.com', password: 'test');
+    expect((await draft.currentUser)?.id, 'draft');
+    expect({for (final key in prefs.getKeys()) key: prefs.get(key)}, before);
+    expect((await active.currentUser)?.id, 'owner');
+    final otherAccount = makeAuth(true, 'draft');
+    final sameAccount = makeAuth(true, 'owner');
+    addTearDown(otherAccount.dispose);
+    addTearDown(sameAccount.dispose);
+    await otherAccount.initialize(expectedEmail: 'draft@example.com');
+    expect(await otherAccount.currentUser, isNull);
+    await sameAccount.initialize(expectedEmail: ' OWNER@example.com ');
+    expect((await sameAccount.currentUser)?.id, 'owner');
+    expect({for (final key in prefs.getKeys()) key: prefs.get(key)}, before);
+  });
+}
diff --git a/test/providers/cloud_session_engine_test.dart b/test/providers/cloud_session_engine_test.dart
new file mode 100644
index 000000000..f8e6aa7bf
--- /dev/null
+++ b/test/providers/cloud_session_engine_test.dart
@@ -0,0 +1,60 @@
+import 'package:drift/native.dart';
+import 'package:flutter_cloud_sync/flutter_cloud_sync.dart';
+import 'package:flutter_riverpod/flutter_riverpod.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:shared_preferences/shared_preferences.dart';
+import 'package:beecount/cloud/cloud_session_manager.dart';
+import 'package:beecount/cloud/sync/sync_providers.dart';
+import 'package:beecount/data/db.dart';
+import 'package:beecount/data/repositories/local/local_repository.dart';
+import 'package:beecount/providers/database_providers.dart';
+import 'package:beecount/providers/sync_providers.dart';
+import '../cloud/sync/_fakes/fake_beecount_cloud_provider.dart';
+
+void main() {
+  TestWidgetsFlutterBinding.ensureInitialized();
+  test('configuration switch closes the cached engine and rejects its old key',
+      () async {
+    SharedPreferences.setMockInitialValues({});
+    final db = BeeDatabase.forTesting(NativeDatabase.memory());
+    var config = const CloudServiceConfig(
+        type: CloudBackendType.beecountCloud,
+        name: 'A',
+        beecountCloudBaseUrl: 'https://a.example');
+    final manager = CloudSessionManager(factory: (_) async {
+      final p = FakeBeeCountCloudProvider();
+      return (provider: p, auth: p.auth);
+    });
+    final container = ProviderContainer(overrides: [
+      databaseProvider.overrideWithValue(db),
+      repositoryProvider.overrideWithValue(LocalRepository(db)),
+      cloudSessionManagerProvider.overrideWithValue(manager),
+      activeCloudConfigProvider.overrideWith((ref) async => config),
+    ]);
+    addTearDown(() async {
+      container.dispose();
+      await manager.dispose();
+      await db.close();
+    });
+    final oldProvider =
+        (await container.read(beecountCloudProviderInstance.future))!;
+    final oldEngine = container.read(syncEngineProvider(oldProvider));
+    container.invalidate(activeCloudConfigProvider);
+    expect(await container.read(beecountCloudProviderInstance.future),
+        same(oldProvider));
+    expect(container.read(syncEngineProvider(oldProvider)), same(oldEngine));
+    config = const CloudServiceConfig(
+        type: CloudBackendType.beecountCloud,
+        name: 'B',
+        beecountCloudBaseUrl: 'https://b.example');
+    container.invalidate(activeCloudConfigProvider);
+    final newProvider =
+        (await container.read(beecountCloudProviderInstance.future))!;
+    expect(newProvider, isNot(same(oldProvider)));
+    expect((await oldEngine.sync(ledgerId: '1')).hasError, isTrue);
+    expect(() => container.read(syncEngineProvider(oldProvider)),
+        throwsStateError);
+    expect(container.read(syncEngineProvider(newProvider)),
+        isNot(same(oldEngine)));
+  });
+}